Radiant fluence from ray tracing in optical multipass systems

In applications of optical multipass cells in photochemical reactors and laser excitation of weak transitions, estimation of the radiation dose in a volume of interest allows to assess the performance and optimize the design of the cell. We adopt radiant fluence as the figure of merit and employ the radiative transfer equation to derive analytical expressions for average radiant fluence in a given volume of interest. These are used to establish practical approximations and a Monte Carlo ray tracing model of the spatial distribution of fluence. Ray tracing is performed with Zemax OpticsStudio 18.9.